Pack min + max into one attribute :muscle:

Some devices supported by Mapbox GL provide only 8 vertex attributes; this change packs existing attributes to get us just under that limit.

For properties using a composite function, pack the min and max values into a single attribute with two logical components instead of using two separate attributes and buffers. Special logic is included for color attributes, whose integer components must be packed into the available bits of floating-point attributes. (We don't have access to ivec types in GL ES 2.0.)

For source functions, continue to bind just a one-component attribute even though the GLSL type is vec2 (or vec4 for colors). The type-checking done by gl::Attribute is relaxed slightly to accommodate this.

1 files changed, 7 insertions, 5 deletions

diff --git a/src/mbgl/shaders/symbol_icon.cpp b/src/mbgl/shaders/symbol_icon.cpp
index 5945f1f3b1..9adda0ba16 100644
--- a/src/mbgl/shaders/symbol_icon.cpp
+++ b/src/mbgl/shaders/symbol_icon.cpp
@@ -7,14 +7,13 @@ namespace shaders {
 
 const char* symbol_icon::name = "symbol_icon";
 const char* symbol_icon::vertexSource = R"MBGL_SHADER(
-attribute vec2 a_pos;
-attribute vec2 a_offset;
+
+attribute vec4 a_pos_offset;
 attribute vec2 a_texture_pos;
 attribute vec4 a_data;
 
 uniform lowp float a_opacity_t;
-attribute lowp float a_opacity_min;
-attribute lowp float a_opacity_max;
+attribute lowp vec2 a_opacity;
 varying lowp float opacity;
 
 // matrix is for the vertex position.
@@ -30,7 +29,10 @@ varying vec2 v_tex;
 varying vec2 v_fade_tex;
 
 void main() {
-    opacity = mix(a_opacity_min, a_opacity_max, a_opacity_t);
+    opacity = unpack_mix_vec2(a_opacity, a_opacity_t);
+
+    vec2 a_pos = a_pos_offset.xy;
+    vec2 a_offset = a_pos_offset.zw;
 
     vec2 a_tex = a_texture_pos.xy;
     mediump float a_labelminzoom = a_data[0];